The goal of this research is to seek identifiable genetic markers whose inheritance is linked with that of multiple endocrine neoplasia, type II (MEN II), and to screen individuals to detect preclinical onset of the disease. Approximately 240 individuals will be screened for a wide variety of genetic markers in the attempt to identify genetic marker loci which are closely linked to the locus at which the cancer gene is segregating. This information will be used to identify individuals at high risk for inheriting the gene. Endocrinological screening is continued in the attempt to detect early manifestations of the disease in sufficient time so that advanced carcinoma can be avoided.